Pool Blok, 5.75" x 2.875" x 2.87", Pool & Spa Cleaner Brick, A Pure Pumice Scouring Stone Cut & Sized For Spot, Surface & Underwater Cleaning Of Recreational Swimming Pools & Spas, Spot Cleaner For Rust Marks, Algae Or Leaf Stains, Pool Blok Quickly Shapes To Any Surface, Concrete, Masonry & Hard Metal Surfaces.